Rfid tag with reduced detuning characteristics

ABSTRACT

An RFID tag and an RFID access card configured to reduce detuning effects from a typical RFID environment. The present invention provides an RFID tag that is specifically configured to reduce the detuning effects caused by initiating communication between an RFID tag and an RFID tag reader in the presence of materials such as metal, liquid, and the human body. In one embodiment, the present invention provides an RFID tag comprising an electronic circuit portion attached to a main antenna body portion, the main antenna body portion having two opposite side portions, which are substantially symmetrical with respect to one another, wherein each side portion extends outwardly to form a generally side-oriented v-shape.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/053,109, filed Mar. 21, 2008, which claims priority to U.S.Provisional Application No. 60/896,780, filed Mar. 23, 2007, both ofwhich are incorporated herein in their entireties by reference.

FIELD OF THE INVENTION

The present invention is directed to automatic identification devicesand more specifically to an RFID tag design that improves antennadetuning.

BACKGROUND OF THE INVENTION

The use of Electronic Article Surveillance, Radio FrequencyIdentification, and electronic security tag technology (hereinaftercollectively referred to as ‘RFID’) is becoming increasingly prevalentin manufacturing, inventory control, retail and residential settings.RFID technology provides efficient, instantaneous communication betweena reader and an RFID tag without direct line-of-sight scanning, as iscommonly required in more conventional automatic identificationtechnologies (e.g., bar-code, optical scanning, etc.). RFID technologyinvolves the transmission of information through radio waves. A typicalRFID system includes an RFID tag and an RFID reader/encoder. First usedmany decades ago in military and espionage applications, RFID technologyis now emerging as a valuable tool in commercial and domestic settings.For example, RFID technology is used by manufacturers or retailers toinstantaneously track product inventories and thereby adjust to specificinventory needs. Similarly, RFID technology can be used by automobilecommuters to pay highway tolls without interrupting their commute, or bypet owners to provide reassurance that pets are readily locatable,regardless of lost collars.

RFID tags typically include an electronic circuit chip and an antennaattached to the circuit chip. The circuit chip and antenna are generallythin, flexible, and mounted to a flexible dielectric substrate. Antennashave numerous configurations and each is structured generally to collectand broadcast electromagnetic energy from a distant reader. RFID chipscan be programmed to store a variety of information. For example, RFIDchips often include retail product identification such as a productserial number. In other applications, relatively more complexinformation may be provided such as biometric information on an employeeID badge. Such applications may include “smart cards,” which include anRFID tag or inlay integrated into the card.

RFID tag and reader systems may operate over a wide range offrequencies, including low-frequency (LF) applications, high-frequency(HF) applications, and ultra-high-frequency applications (UHF). LFapplications typically operate from 125-148.5 kHz. HF applicationstypically operate at 13.56 MHz. UHF applications typically operate from300 MHz to 3GHz. The “read range” of an RFID tag and reader system isoften defined as the distance from which a reader can communicate with atag. Read ranges can be affected by variety of factors. For example,active RFID tags (as opposed to passive RFID tags) have independentpower sources (typically batteries), and have relatively longer readrange. However, active RFID tags are more expensive and may be lessreliable than passive RFID tags due to the need to replace the battery.In theory, passive RFID tags have an infinite life, but offer shorterread ranges.

Passive LF and HF applications offer very short read ranges, oftenrequiring the RFID tag to be within 1 to 12 inches of a reader forsuccessful communication. Passive UHF applications typically offerlonger read ranges, allowing RFID tags to be within 2 to 5 meters ormore of a reader for successful communication. However, variousenvironmental factors can detune an RFID tag, thus modifying theoperating frequency and potentially affecting the read range of the RFIDtag. RFID tags in the presence of metals and liquids may experiencedetuning due to absorption or parasitic capacitance provided by thesematerials.

Additionally, due to the high water content of the human body, a usermay detune an RFID tag simply by using it. This is especiallytroublesome for RFID tags (inlays) imbedded within access cards that areheld by a user when read by a reader. For example, in certain instances,a user may unknowingly detune an RFID access card by obscuring the cardwhile attempting to hold the card near a reader. In other instances, auser may detune an RFID access card by wearing the card on a lanyardsuch that the card is adjacent the user's body. Although strategichandling of the access card may reduce the detuning effect (such ashandling the card only by its edges or extending the card away from theuser's body), these solutions defeat the convenience and speedadvantages provided by RFID technology.

As a result, there is a need for an improved RFID tag design thatreduces various detuning effects, including that of a user handing anRFID tag in the presence of a reader.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above needs and others by providingan RFID tag configured to reduce detuning effects from a typical RFIDenvironment. More specifically, the present invention provides an RFIDtag and an RFID access card that are specifically configured to reducethe detuning effects caused by attempting communication with an RFID tagin the presence of materials such as metal, liquid, and the human body.

In one embodiment, the present invention provides an RFID tag comprisingan electronic circuit attached to a main antenna body. The main antennabody defines a center through which an imaginary pair of first andsecond perpendicular axes intersect and comprises two opposite sideportions, wherein each side portion is substantially symmetrical withrespect to itself about the second imaginary axis, and wherein each sideportion extends outwardly from the first imaginary axis along the secondimaginary axis to form a generally side-oriented v-shape, defined byupper and lower angled edges and upper and lower side edges, and whereinthe main antenna body further comprises an elongate first slot thatextends from the center of the main antenna body, substantially alongthe second imaginary axis, and a second slot substantially perpendicularto and intersecting the first slot proximate the center of the mainantenna body.

In another embodiment, the RFID tag may operate on the UHF range. Inanother embodiment, the upper and lower angled edges may extend from thefirst imaginary axis at a substantially constant angle α. The angle αmay be in the range of about 10° to about 85°, and may preferably be inthe range of about 40° to about 85°. In another embodiment, theelectronic circuit may be attached proximate the intersection of thefirst and second slots. In another embodiment, the upper and lower sideedges are separated by a notch substantially located along the secondimaginary axis, wherein the notch separating the upper and lower sideedges may have a side oriented v-shape defined by an upper notch edgeand a lower notch edge, wherein the upper notch edge is substantiallyparallel to the upper angled edge and the lower notch edge issubstantially parallel to the lower angled edge.

In another embodiment, the elongate slot may define a slot half-length,wherein the slot half-length may be in the range of about 5 mm to about30 mm (i.e., about 10 mm to about 50 mm for the full length of theslot), and may preferably be in the range of about 15 mm to 25 mm. Inanother embodiment, the elongate slot may define a slot height, whereinthe slot height may be in the range of about 0.5 to about 5 mm, and maypreferably be approximately 1 mm. In another embodiment, the RFID tagfurther comprises a back plate located on one side of the RFID tag andconfigured to shield the RFID tag. The back plate may be comprised of ametal material. In still another embodiment, the present inventionprovides an RFID tag comprising an electronic circuit attached to a mainantenna body, the main antenna body defining a center through which animaginary pair of first and second perpendicular axes intersect andcomprising two opposite side portions, wherein each side portion issubstantially symmetrical with respect to itself about the firstimaginary axis, and wherein each side portion extends outwardly from thecenter along the second imaginary axis to form a shape having arelatively large surface area, and wherein the main antenna body furthercomprises an elongate first slot that extends from the center of themain antenna body, substantially along the second imaginary axis, and asecond slot substantially perpendicular to and intersecting the firstslot proximate the center of the main antenna body. In anotherembodiment, the RFID tag further includes a back plate comprised of ametal material located on one side of the RFID tag and configured toshield the RFID tag. In another embodiment, each side portion of themain antenna body extends outwardly from the first imaginary axis alongthe second imaginary axis to form a generally side-oriented v-shape,wherein the opposite side portions further comprise convex upper edges,each defining respective vertex points.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus described the invention in general terms, reference will nowbe made to the accompanying drawings, which are not necessarily drawn toscale, and wherein:

FIG. 1 shows a user attempting to initiate communication between a priorart UHF RFID access card and an associated RFID access card reader;

FIG. 2 shows an RFID tag having reduced detuning characteristics inaccordance with one embodiment of the present invention;

FIG. 3 shows an RFID tag having reduced detuning characteristics inaccordance with one embodiment of the present invention;

FIG. 4 is a detailed view showing an electronic circuit attached to amain antenna body in accordance with one embodiment of the presentinvention;

FIG. 5 is a detailed view showing an electronic circuit attached to amain antenna body in accordance with one embodiment of the presentinvention;

FIG. 6 shows a perspective view of an RFID access card that includes anRFID tag having reduced detuning characteristics in accordance with oneembodiment of the present invention;

FIG. 7 shows a user initiating communication between an RFID access cardand an associated RFID access card reader, the RFID access cardincluding a UHF RFID tag having reduced detuning characteristics inaccordance with one embodiment of the present invention;

FIG. 8 shows an RFID tag with a back plate in accordance with anotherembodiment of the present invention;

FIG. 9 shows an RFID tag in accordance with another embodiment of thepresent invention;

FIG. 10 is a detailed view showing a center area of an RFID tag inaccordance with one embodiment of the present invention;

FIG. 11 shows an RFID tag in accordance with another embodiment of thepresent invention; and

FIG. 12 is a detailed view showing a center area of an RFID tag inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, the present inventionmay be embodied in many different forms and should not be construed aslimited to the embodiments set forth herein; rather, these embodimentsare provided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Security access points, such as those located in office buildings andthe like, often employ RFID technology. Typical applications includeRFID access cards configured to be read by RFID access card readers.These access cards are issued to authorized users and allow the users togain access through various security access points. To gain accessthrough a typical security access point, a user may grasp and bringhis/her access card in close proximity to an associated access cardreader. In some instances, a user may hang his/her access card from alanyard worn around the user's neck. In other instances, a user mayattach his/her access card to a retractable device attached to theuser's clothing. In any event, the user's body may have a detuningeffect on an RFID tag located within the access card.

FIG. 1 shows prior art RFID access card 10 held by a user 12 in closeproximity to an RFID access card reader 14. The RFID access card 10includes an RFID tag 16 comprising an electronic circuit 18 and anantenna 20. The RFID access card of FIG. 1 operates in the UHF range andemploys a passive RFID tag 16. As shown in the figure, the antenna 20 ofthe prior art RFID access card 10 extends in an approximate oval orrounded rectangular shape around the periphery of the access card 10,with the electronic circuit 18 located on one end of the card 10. A user12 using a prior art RFID access card 10 in the manner shown in thedrawing would likely detune the RFID tag 16 with his/her hand byobscuring and/or being in close contact with a large portion of theperimeter-oriented antenna 20. The result of such detuning would requirethe user 12 to reorient the access card 10 and/or to bring the accesscard 10 even closer to the access card reader 14. Although not shown inthe figure, a user wearing an RFID access card 10 against his/her bodyon a lanyard or other retractable device would likewise detune the RFIDtag 16 either by handling the access card 10 with his/her hands toinitiate communication between the reader 14 and the card 10, or byattempting to initiate communication between the reader 14 and theaccess card 10 with the card abutting the user's body. In any event,requiring a user to reorient or otherwise reattempt communicationbetween the access card 10 and the card reader 14 defeats the advantagesprovided by RFID technology.

The present invention addresses these concerns and others by providingan RFID tag that is configured to reduce common environmental detuningeffects. As will be discussed in more detail below, the structure of theRFID tag of various embodiments of the present invention is especiallyoptimized to reduce the detuning effects commonly caused by the handlingof UHF RFID tags (and access cards utilizing said tags) duringcommunication with a reader. In accordance with these and otherobjectives, the inventor of the present invention has determined thatRFID tags configured as described in more detail below, provide improvedcommunication with a reader when handled or otherwise subjected tocommon human and other environmental detuning effects. In certaininstances, an RFID tag configured according to an exemplary embodimentof the present invention may provide as much as 50% better performancethan conventional tag designs.

FIG. 2 shows an RFID tag 100 in accordance with one embodiment of thepresent invention. The RFID tag 100 of the depicted embodiment includesan electronic circuit 102 and a main antenna body 104. The electroniccircuit 102 of the depicted embodiment is of a type typically used inUHF RFID applications, and may have a variety of configurations,including, but not limited to, a dual terminal configuration, an exampleof which is depicted in FIG. 4, or a single terminal configuration, anexample of which is depicted in FIG. 5. Such electronic circuits areavailable from a variety of manufacturers including, but not limited to,electronic RFID circuits provided by Impinj, Inc, such as the Monza™ Gen2 tag chip, and the G2XM circuit provided by NXP Semiconductors. Thesecircuits may also be referred to as microcircuits, IC's, silicon chips,microcircuits, computer chips, chips, etc. The main antenna body 104 ofthe depicted embodiment of the present invention defines a center 106.Two imaginary axes, a first axis 108 and a second axis 110, extendthrough the center 106 substantially perpendicular to each other.

The main antenna body 104 comprises two side portions 112, 114. The mainantenna body side portions 112, 114 are substantially symmetrical withrespect to one another about the first imaginary axis 108, and each sideportion 112, 114 is substantially symmetrical with respect to itselfabout the second imaginary axis 110. Each of the main antenna body sideportions 112, 114 forms a general side oriented v-shape defined by upperangled edges 116, 118, lower angled edges 120, 122, upper side edges124, 126, and lower side edges 128, 130. The upper and lower anglededges 116, 118 and 120, 122 extend outwardly from the first imaginaryaxis 108 at an angle α relative to the first imaginary axis 108 from anarea proximate the center 106 of the main antenna body 104. A distance131 between the side edges 124, 128 and 126, 130 defines an overall taglength. The upper side edges 124, 126 and the lower side edges 128, 130are separated by notches 132, 133, which are substantially located alongthe second imaginary axis 110. In the depicted embodiment, each notch132, 133 has a general side-oriented v-shape defined by upper notchedges 134, 136 and lower notch edges 138, 140. It should be noted,however, that in other embodiments, the shape of the notch may bevaried, for example, the notch may have a curved u-shape, a squaredu-shape, a partial circular profile, etc. The main antenna body 104 alsoincludes an elongate first slot 142 that extends outwardly substantiallyalong the second imaginary axis 110. A second slot 144 is locatedsubstantially along the first imaginary axis 108 and intersects thefirst slot 142 proximate the center 106 of the main antenna body 104. Inthe depicted embodiment, the configuration of the main antenna body 104serves to distribute antenna material radially outward from theelectronic circuit in a certain pattern thus decreasing typical detuningeffects. Although desiring not to be bound by any particular theory, ineffect, the structure of the main antenna body 104 of the presentinvention behaves similar to two separate antennas separated by thefirst imaginary axis 108. In reality the two sides are not completelyindependent, however they behave that way when one side is subject to adetuning condition. Although the depicted embodiment of the presentinvention shows side portions that have a general side-oriented v-shape,in other embodiments the side portions may have any other configurationhaving relatively large surface areas that extend from the center 106,including, but not limited to, diamond shaped side portions and circularshaped side portions. Furthermore, although not shown in the figures,side portions of an RFID tag in accordance with other embodiments of thepresent invention may be tuned slightly differently. For example oneside may be tuned to a particular operating frequency (e.g., 920 MHz)and the other side may be tuned to a different operating frequency(e.g., 905 MHz), thus extending the overall bandwidth. The two sidescould also be tuned to different regulatory environments. For example,one side could be tuned to EU (e.g, 868 MHz) and the other could betuned to Japan (e.g., 950 MHz). In such embodiments, the side portionsmay have different shapes, such as where an angle α on one side isdifferent than an angle α′ on the other. Additionally, the slothalf-length could be different for each side.

FIG. 3 shows an alternative embodiment of RFID tag 100 in accordancewith one embodiment of the present invention. The RFID tag 100 of thedepicted embodiment includes an electronic circuit 102 which may have avariety of configurations, and a main antenna body 104. The main antennabody 104 of the depicted embodiment of the present invention defines acenter 106. Two imaginary axes, a first axis 108 and a second axis 110,extend through the center 106 substantially perpendicular to each other.

The main antenna body 104 comprises two side portions 112, 114. The mainantenna body side portions 112, 114 are substantially symmetrical withrespect to one another about the first imaginary axis 108, and each sideportion 112, 114 is substantially symmetrical with respect to itselfabout the second imaginary axis 110. Each of the main antenna body sideportions 112, 114 forms a general v-shape defined by upper angled edges116, 118, lower angled edges 120, 122, and side edges 300, 302. Theupper and lower angled edges 116, 118 and 120, 122 extend outwardly fromthe first imaginary axis 108 at an angle α relative to the firstimaginary axis 108 from an area proximate the center 106 of the mainantenna body 104. A distance 131 between the side edges 300, 302 definesan overall tag length. The main antenna body 104 also includes anelongate first slot 142 that extends outwardly substantially along thesecond imaginary axis 110. A second slot 144 is located substantiallyalong the first imaginary axis 108 and intersects the first slot 142proximate the center 106 of the main antenna body 104. In the depictedembodiment, the configuration of the main antenna body 104 serves todistribute antenna material radially outward from the electronic circuitin a certain pattern thus decreasing typical detuning effects. Althoughdesiring not to be bound by any particular theory, in effect, thestructure of the main antenna body 104 of the present invention behavessimilar to two separate antennas separated by the first imaginary axis108. In reality the two sides are not completely independent, howeverthey behave that way when one side is subject to a detuning condition.

FIG. 4 shows an exemplary detailed view of the main antenna body 104 foran electronic circuit 102 that is a dual-terminal electronic circuit.Note that while FIG. 4 describes aspects of RFID tag 100, thedescription can refer to aspects any RFID tag embodiment in accordancewith the present invention. The elongate first slot 142 includes aninner portion 146 that connects two side slot portions 148, 150. Theelongate first slot 142 also defines a slot half-length 152 and a slotheight 154 (both shown in FIG. 2). The second slot 144 defines a secondslot width 156. The inner portion 146 defines an inner portion height160. As shown in the figure, the electronic circuit 102 attaches to themain antenna body 104 proximate the center 106 and across theintersection of the inner portion 146 and the second slot 144. Theelectronic circuit 102 of the depicted embodiment includes four ports,A1, A2, and grounds G, G, which are attached to the main antenna body104 as shown.

FIG. 5 shows another exemplary detailed view of the main antenna body104 for an electronic circuit 102 that is a single-terminal electroniccircuit. Note that while FIG. 5 describes aspects of RFID tag 100, thedescription can refer to aspects any RFID tag embodiment in accordancewith the present invention. The elongate first slot 142 includes aninner portion 146 that connects two side slot portions 148, 150. Theelongate first slot 142 also defines a slot half-length 152 and a slotheight 154 (both shown in FIG. 2 and FIG. 3). The second slot 144 can bedefined by tabs 500, 502. The second slot 144 defines a second slotwidth 156. Second slot width 156 may be a width between tab 500 and tab502 with respect to the axis 110. The inner portion 146 defines an innerportion height 160. In some embodiments, the inner portion height 160may be equivalent to the slot height 154. As shown in the figure, theelectronic circuit 102 attaches to the main antenna body 104 proximatethe center 106 and across the second slot 144. The electronic circuit102 of the depicted embodiment includes two ports, A and G, which areattached to the main antenna body 104 via tabs 500, 502 as shown.

As shown in FIG. 6, an RFID tag 100 in accordance with variousembodiments of the present invention may be configured to be used inconnection with an RFID access card 162. Note that while FIG. 6 depictsRFID tag 100, any RFID tag embodiment in accordance with the presentinvention may be used as the RFID tag described with respect to FIG. 6.In such embodiments, the RFID tag 100 represents an inlay within cardsubstrate 164. A top laminate 166 may be placed above the RFID tag 100to protect the electronic circuit 102 and antenna body 104 componentsand provide a surface receptive to printing. In the depicted embodiment,the RFID tag 100 is approximately 3 to 9 mils (i.e., 75 to 225 microns(μm)) thick. The depicted embodiment shows a simplified version of anRFID access card. In other embodiments, an RFID access card may includefive layers, including a protective top layer constructed of a PET, PVC,or other similar material, a PVC intermediate layer, an RFID inlay on aPET layer, another PVC intermediate layer, and a bottom protective layerconstructed of PET, PVC, or other similar material. Locating theelectronic circuit 102 proximate the center 106 of the main antenna body104 and providing side portions 112, 114 aids in providing lessorientation dependence than prior art access cards where the electroniccircuit may be located on one end of the access card. Additionally, aswill be discussed below, the specific configuration of the main antennabody 104 further improves detuning performance.

In order to determine an optimal configuration for reducing detuningeffects, several parameters involved in the design and manufacture of aUHF RFID access card may be chosen. Such parameters include, but are notlimited to, the configuration of the antenna, the impedance of theelectronic circuit, the composition of the chip attachment adhesive, theantenna material (e.g, silver ink, copper, aluminum, etc), the antennamaterial thickness and conductivity, the antenna substrate thickness anddielectric constant, the card laminate material (e.g, PVC, PET,polycarbonate, etc.), the laminate material thickness and dielectricconstant, and variations within the frequency range of the regulatoryenvironment (e.g, U.S.: 902-928 MHz, EU: 866-868 MHz, Japan: 950-956MHz). The inventor of the present invention has determined thatconfiguring an RFID tag as shown in the figures and as described in theclaims, substantially reduces the detuning effects caused by typicalenvironmental conditions, despite variations in the other parameters.

Referring back to FIG. 2 and FIG. 3, an antenna configuration for anoptimized RFID tag 100 in accordance with one exemplary embodiment ofthe present invention is shown. Note that while the configurationparameters described below refer to RFID tag 100, any RFID tagembodiment in accordance with the present invention may include theconfiguration parameters described below. By configuring an RFID tag 100in accordance with this exemplary embodiment of the present invention,better communication between the RFID tag 100 and a tag reader may beachieved. In the exemplary embodiment, the upper 116, 118 and lower 120,122 angled edges of the main antenna body 104 extend from the firstimaginary axis 108 at a constant angle α that is between about 10° andabout 85° and is preferably between about 40° and about 85°. In someembodiments, α may be 65°. The tag length 131 is approximately 80 mm,which allows the RFID tag 100 to be used as an inlay for an accessbadge, the standard length of which is typically about 86 mm. The slotheight 154 of the depicted embodiment is between about 0.5 mm and about5 mm and is preferably about 1 mm. The slot half length 152 (i.e., thelength from the first imaginary axis 108 of each side portions 148, 156)is between about 10 mm and about 50 mm, and is preferably between about15 mm and about 25 mm. The second slot width 156 and the inner portionheight 160 are both approximately 350 μm. Although not referenced in thefigure, the overall height of the RFID tag 100 of the depictedembodiment of the present invention is approximately 42 mm. Withreference to FIG. 2, each notch is approximately 8 mm in height, and hasan approximate length of 9 mm. It should be noted that although theabove describes the approximate dimensions of the depicted embodiment,many other configurations within the scope of the present invention arepossible.

Referring to FIG. 7, an access card 162 having an RFID tag 100configured according to an exemplary embodiment of the present inventionis shown being used by a user 12 in a similar manner as shown withrespect to the prior art access card 10 of FIG. 1. Note that while FIG.7 depicts RFID tag 100, any RFID tag embodiment in accordance with thepresent invention may be used as the RFID tag described with respect toFIG. 7. In the depicted embodiment, however, the detuning effects causedby the user's hands are reduced due to the optimized configuration ofthe RFID tag 100. Regardless of the manner in which the user handles theaccess card 162, the configuration of the RFID tag 100 allows improvedcommunication between the access card reader 14 and the access card 162.Likewise, although not shown in the figure, an access card 162 inaccordance with an exemplary embodiment placed on a lanyard or otherretractable device also provides better communication between the accesscard reader 14 and the access card 162 by reducing the detuning effectsof a user's body. In certain instances, an

RFID tag 100 configured according to an exemplary embodiment of thepresent invention may provide 30%-50% better performance thanconventional tag designs.

FIG. 8 shows another embodiment of the present invention. In thedepicted embodiment, an additional component comprising a back plate 168may be added behind the RFID tag 100. Note that while FIG. 8 depictsRFID tag 100, any RFID tag embodiment in accordance with the presentinvention may be used as the RFID tag described with respect to FIG. 8.In various embodiments, the back plate 168 may be comprised of a thinfilm of metal material, including, but not limited to, aluminum, copper,etc. The back plate 168 serves to shield electromagnetic radiation fromone direction of the RFID tag. An embodiment such as this may beparticularly advantageous for use with metal objects and/or objects thatcontain liquid, or for access cards attached to a lanyard and wornaround a user's neck. As noted above, materials such as metal, liquid,and the human body tend to detune the RFID tag. By utilizing a backplate 168 in accordance with various embodiments of the presentinvention, electromagnetic waves are directed away from the back plate168. As a result, a back plate 168 may be placed between the object (orin the case of an access card, the user's body) and the RFID tag 100,thus further decreasing detuning effects caused by the user or theobject.

In the depicted embodiment, the back plate 168 is a similar material tothe RFID tag 100, for example silver ink, copper, aluminum, etc. Thethickness of the back plate 168 of the depicted embodiment isapproximately 10 to 35 microns and it is separated from the RFID tag 100by a distance of about 0.5 mm to about 3 mm. In various embodiments, theback plate may be separated from the RFID tag 100, by a dielectriclayer. The dielectric layer may be made of PET, PVC, or other similarmaterial. In various embodiments, the dielectric layer may have athickness of about 0.5 mm to about 3 mm and may be any type of substancehaving a dielectric constant between 1 and 10.

FIG. 9 shows an RFID tag 900 in accordance with another embodiment ofthe present invention. The RFID tag 900 of the depicted embodiment ofthe present invention defines a center 906. Two imaginary axes, a firstaxis 908 and a second axis 910, extend through the center 906substantially perpendicular to each other.

In the depicted embodiment, the RFID tag 900 comprises two side portions912, 914. The side portions 912, 914 are substantially symmetrical withrespect to one another about the first imaginary axis 908. Each of theside portions 912, 914 forms a general side oriented v-shape defined byfirst upper angled edges 916, 918, second upper angled edges 917, 919lower angled edges 920, 922, upper side edges 924, 926, and lower sideedges 928, 930. The first upper angled edges 916, 918 extend outwardlyfrom the first imaginary axis 908 at an angle β relative to the firstimaginary axis 908 from an area proximate the center 906 of the RFID tag900. The second upper angled edges 917, 919 extend outwardly from thefirst imaginary axis 908 at an angle φ relative to the first imaginaryaxis 908 from upper edge vertex points 921, 923. In some embodiments,the angle φ may have a measured value greater than the measured valuefor the angle β. As a result, first upper angled edges 916, 918 andsecond upper angled edges 917, 919 may combine to create a convex edgeon the upper edge of side portions 912, 914.

The lower angled edges 920, 922 extend outwardly from the firstimaginary axis 108 at an angle relative to the first imaginary axis 108.Lower angled edges 920, 922 need not be linear edges and may include avertex point where the angle of the lower edge changes. A distance 931may be a maximum between the side edges 924, 928 and 926, 930, and maydefine an overall tag length. The upper side edges 924, 926 and thelower side edges 928, 930 may have an angle with respect to the secondimaginary axis 910 such that upper side edge 924 and lower side edge 928create a concave edge, and upper side edge 926 and lower side edge 930create a concave edge. It should be noted, however, that in otherembodiments, the shape of the upper side edges 924, 926 and lower sideedges 928, 930 may be varied creating an overall side edge may have acurved u-shape, a squared u-shape, a partial circular profile, etc. TheRFID tag 900 also includes an elongate first slot 942 that extendsoutwardly substantially along the second imaginary axis 910. A secondslot 944 is located substantially along the first imaginary axis 908 andintersects the first slot 942 proximate the center 906 of the RFID tag900.

In the depicted embodiment, the configuration of the RFID tag 900 servesto distribute antenna material radially outward from the center point906 in a certain pattern thus decreasing typical detuning effects.

FIG. 10 shows an exemplary detailed view of the RFID tag 900. Theelongate first slot 942 includes an inner portion 946 that connects twoside slot portions 948, 950. The elongate first slot 942 also defines aslot half-length 952 and a slot height 954. The second slot 944 definesa second slot width 956. An electronic circuit (not pictured) may belocated proximate the center 906 and across the intersection of theinner portion 946 and the second slot 944.

FIG. 11 shows an RFID tag 1100 in accordance with another embodiment ofthe present invention. The RFID tag 1100 of the depicted embodiment ofthe present invention defines a center 1106. Two imaginary axes, a firstaxis 1108 and a second axis 1110, extend through the center 1106substantially perpendicular to each other.

In the depicted embodiment, the RFID tag 1100 comprises two sideportions 1112, 1114. The side portions 1112, 1114 are substantiallysymmetrical with respect to one another about the first imaginary axis1108. Each of the side portions 1112, 1114 forms a general side orientedv-shape defined by upper angled edges 1116, 1118, side edges 1124, 1126,and lower angled edges 1120, 1122. The upper angled edges 1116, 1118extend outwardly from the first imaginary axis 1108 at an angle θrelative to the first imaginary axis 1108 from an area proximate thecenter 1106 of the RFID tag 1100. Upper angled edges 1116, 1118 need notbe linear edges and may include a vertex point where the angle of theupper edge changes.

The lower angled edges 1120, 1122 extend outwardly from the firstimaginary axis 1108 at an angle relative to the first imaginary axis1108. Lower angled edges 1120, 1122 need not be linear edges and mayinclude a vertex point where the angle of the lower edge changes. Adistance 1131 between the side edges 1124 and 1126 may define an overalltag length. Side edges 1124, 1126 need not be linear edges and mayinclude a vertex point where the angle of the side edge changes. TheRFID tag 1100 also includes an elongate first slot 1142 that extendsoutwardly substantially along the second imaginary axis 1110. A secondslot 1144 is located substantially along the first imaginary axis 1108and intersects the first slot 1142 proximate the center 1106 of the RFIDtag 1100.

In the depicted embodiment, the configuration of the RFID tag 1100serves to distribute antenna material radially outward from the centerpoint 1106 in a certain pattern thus decreasing typical detuningeffects.

FIG. 12 shows an exemplary detailed view of the RFID tag 1100. Theelongate first slot 1142 includes an inner portion 1146 that connectstwo side slot portions 1148, 1150. The elongate first slot 1142 alsodefines a slot half-length 1152 and a slot height 1154. The second slot1144 defines a second slot width 1156. An electronic circuit (notpictured) may be located proximate the center 1106 and across theintersection of the inner portion 1146 and the second slot 1144. Sidechannels 1180, 1182 define a channel width 1184. Connecting areas 1186,1188 may connect the material surrounding elongate first slot 1142 toside portions 1112, 1114. Connecting areas 1186, 1188 may located at anyposition within side channels 1180, 1182 such that connecting areascreate a connection between the material surrounding elongate first slot1142 and side portions 1112, 1114. Various locations of connecting area1186, 1188 may affect the tuning of RFID tag 1100. Upper gap 1190 andlower gap 1192 may define gap width 1194.

Many modifications and other embodiments of the invention set forthherein will come to mind to one skilled in the art to which thisinvention pertains having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. An RFID tag, the RFID tag comprising: an electronic circuit attachedto a main antenna body, the main antenna body including: a first sideantenna portion; a second side antenna portion; at least one connectingarea; and an inner antenna portion, the inner antenna portion defining:a first slot substantially surrounded by the inner antenna portion; asecond slot that channels through the inner antenna portion; a firstside channel substantially between the first side antenna portion andthe inner antenna portion; and a second side channel substantiallybetween the second side antenna portion and the inner antenna portion,wherein the at least one connecting area connects the inner antennaportion to at least one of the first side antenna portion and the secondside antenna portion.
 2. The RFID tag of claim 1, wherein the at leastone connecting area comprises: a first connecting area that connects theinner antenna portion to the first side antenna portion; and a secondconnecting area that connects the inner antenna portion to the secondside antenna portion.
 3. The RFID tag of claim 1, wherein the at leastone connecting area defines a side of at least one of the first sidechannel and the second side channel.
 4. The RFID tag of claim 3, whereinthe location of the at least one connecting area affects tuning of theRFID tag.
 5. The RFID tag of claim 1, wherein the first side antennaportion, the second side antenna portion, the at least one connectingarea, and the inner antenna portion are comprised of one or moreelectrically conductive materials.
 6. The RFID tag of claim 1, whereinthe first slot that defines a first slot half-length and a first slotheight, wherein the first slot half-length is greater than the firstslot height such that the first slot has an elongated shape.
 7. The RFIDtag of claim 6, wherein the second slot intersects the first slot. 8.The RFID tag of claim 1, wherein the first slot is comprised of an innerportion that connects a first side slot portion and a second side slotportion.
 9. The RFID tag of claim 1, wherein the electronic circuit ispositioned proximate the center of the first slot.
 10. The RFID tag ofclaim 9, wherein the electronic circuit at least partially spans wherethe first slot and the second slot intersect.
 11. The RFID tag of claim1, wherein: the first side channel defines a first side channel width;the second side channel defines a second side channel width; and thefirst side channel width and the second side channel width aresubstantially the same.
 12. The RFID tag of claim 1, wherein the firstside antenna portion, the second side antenna portion, and the innerantenna portion are substantially symmetrical about a first axis. 13.The RFID tag of claim 1, wherein the first side antenna portion and thesecond side antenna portion extend outwardly from the inner antennaportion to form a generally side-oriented v-shape.
 14. The RFID tag ofclaim 1, wherein the RFID tag operates in the UHF range.
 15. The RFIDtag of claim 1 further including a back plate comprised of a metalmaterial located on one side of the RFID tag and configured to shieldthe RFID tag.
 16. The RFID tag of claim 15 further including adielectric layer between the metal material and the main antenna body.17. The RFID tag of claim 1, wherein the RFID tag is incorporated intoan RFID access card, the RFID access card comprising a card substrate towhich the RFID tag is attached.
 18. The RFID access card of claim 17further including a back plate located on one side of the RFID tag andconfigured to shield the RFID tag.
 19. The RFID access card of claim 18further including a dielectric layer between the back plate and the mainantenna body.
 20. The RFID access card of claim 19, wherein a thicknessof the dielectric layer is in the range of 0.5 mm to about 3.0 mm and adielectric constant of the dielectric layer is in the range of 1 toabout 10.